In China, fertilizer input is an important link in facility agriculture production, and has common features of excessive application amount, application of raw organic fertilizers, and uncoordinated N—P—K ratio. Because fertilizer input within a short time has significant yield increasing effect, in order to pursue high output, excessive fertilizers are usually applied, which greatly exceeds actual absorption by crops. As a consequence, residual fertilizers in the soils become a major source of salt ions, which results in the problems of year-to-year exacerbated facility soil secondary salinization, soil microbial flora imbalance, and soil compaction, causes gradually exacerbated environmental quality conditions of facility vegetable soils, and poses a threat to sustainable production capacity of soils and sustainable development of facility vegetable industry.
The salt ions of facility secondary salinized soils comprises four cations K+, Ca2+, Na+, Mg2+ and four anions NO3−, SO42−, Cl−, HCO3−. Research has shown that NO3− in facility soils has the highest content, and proportions of other ions vary with the type of chemical fertilizers and organic fertilizers applied.
The uncoordinated salt ion ratio in facility soils affects the ion balance in crops and hampers the nutrient uptake by crops, thereby affecting the growth and decreasing the yield. The high concentration of salt components inhibits soil microbial activity and affects the effectuation process of soil nutrients, thereby indirectly affecting nutrient supply of soils for crops. The high NO3− content in soils further affects the contents of nitrates and nitrites in crops, thereby reducing the product quality. Nitrate nitrogen partially penetrates into a deep ploughing layer or flows into an underground water, thereby causing water pollution and endangering human health.
Soil microbial growth and propagation require good soil fertility conditions and environmental quality conditions, and the optimum temperature, humidity and nutrients needed are similar to those needed by plants. Therefore, the microbial amount has a close relation with soil fertility and plant growth, can sensitively reflect differences among various soil ecosystems, and thus can used as an important indicator on soil fertility quality. The microbial amount in facility secondary salt salinized soils is significantly reduced, the type and amount of dominant populations are reduced, pathogens such as Pythium are substantially enriched, and pests and diseases are seriously increased, indicating worsened both soil fertility and quality.
To sum up, the problems such as salt accumulation in facility soils and microbial flora imbalance have seriously affected sustainable development of facility cultivation.
Conventional methods such as application of gypsum, organic fertilizers as modifier can be used for adjusting soil properties, and measures such as cultivation of salt-tolerant crops and irrigation and drainage can be taken to discharge salts from soils.
Because of quick action, low cost and easy application, gypsum (CaSO4) has become the most commonly used method in modification of facility soils. The common practice is to apply gypsum onto the soil surface and perform conventional cultivation. Eventually, gypsum will be dissolved in soils, and brought into soil water by irrigation or precipitation. Through ion exchange, calcium ions can replace base ions in soils, and finally are discharged with water from soils. However, gypsum (CaSO4) has numerous disadvantages. For example, gypsum itself is a sparingly soluble substance, so that part of the ions dissolved in soils possibly cannot achieve effective ion exchange for deep soils. In addition, that part of the base ions replaced by gypsum (CaSO4) can be rinsed into underlying soils from crop root zones only by irrigation or precipitation, and can be discharged from the soil body only under good drainage conditions. Moreover, gypsum (CaSO4) itself also is a salt, and in case of multiple repeated use, soil salts will be increased while soils are modified.
Application of organic fertilizers can increase the total amount of soil microorganisms, increase the number of dominant populations, enrich the colony diversity, and stabilize the colony structure. When the fertilization structure comprises a low content of organic fertilizers, increase in proportion of organic fertilizers can significantly inhibit soil salt accumulation. However, improper use of organic fertilizers generates multiple base ions, and substantial application of organic fertilizers also causes soil salt accumulation. For example, application of organic fertilizers such as a rapeseed cake fertilizer that have a low C/N ratio will significantly increase the total salt content in the 0-20 cm soil layer.
Research has shown that for more than 3 years of continuous facility cultivation, soil secondary salinization will occur, which results in decreased crop yield and even crop death, as well as complete loss of soil ploughing capacity. In order to effectively solve the problem of soil secondary salinization, microbial techniques can be introduced. Biological soil modifiers can increase the amount of beneficial microbes in soils, improve the soil structure, decrease the soil bulk density, change the physicochemical properties of soils, adjust water, fertilizer, gas, thermal conditions of soils, and finally achieve the soil quality increasing effect.
CN00999667A titled “Facility Vegetable Soil Modifier and Preparation and Use Thereof” has introduced a soil modifier with peat, kieselguhr, microbial agents (Bacillus subtilis, Actinomycetes and Trichoderma), peanut meal and fly ash as raw materials.
CN101941854A titled “Facility Vegetable Soil Modifier Compatible with CO2 Fertilization and Preparation thereof” has introduced an organic fertilizer obtained by fermenting crop straws with microbial agents (straw decomposing agents and B. subtilis).
CN200610130054.5 titled “Biological Soil Additive Formulation for Overcoming Vegetable Continuous Cropping Obstacles” has introduced a biological soil additive formulated from Trichoderma as functional microbial agent, Vesicular Arbuscular (VA) mycorrhizas, inorganic nonmetallic mineral zeolites, fermented organic fertilizers, hulls, calcium superphosphate and urea.
CN201110078418.0 titled “Biological Organic Fertilizer for Preventing Soil Salinization in Protected Fields” has introduced a biological organic fertilizer produced from microbial (Clostridium thermocellum, Bacillus licheniformis, Lactobacillus acidophilus and Streptomyces badius) fermentation lignite, vinegar residue, sawdust (straw), shale.
CN201210225968.5 titled “Greenhouse, Shed Soil Reducing, Disinfecting Composite Microbial Agent and Soil Disinfection Method” has provided a soil disinfection method, which specifically comprises after crops are harvested, spreading crop straws, organic fertilizers and composite microbial agents (Bacteria, actinomycetes, yeasts, molds) at the ground; deep ploughing soil layers to make small high ridges; coving ridge surfaces with plastic membranes, filling with water under the membranes to reach 100% of soil moisture, sealing the membranes, covering with shed plastic films for 20-25 days; and opening the shed plastic films for ventilation and removing the membranes.
Research has shown that salt accumulation in facility secondary salt salinized soils results in too high osmotic pressure of soils, and thus results in microbial cells cannot perform normal metabolic activity because of excessive dehydration. Thus, the microbial agents in the patients described above possibly cannot perform normal activity or even will die after entering the soils.